Submersible structures

ABSTRACT

A submersible structure floatable to a desired location and sinkable to rest on the water bed, comprising containers on a base, a perimeter wall on the base, and a column extending from the base to above water level, the containers, wall and column being formed of reinforced concrete.

United States Patent Birdy et a1. 9 June 3, 1975 [54] SUBMERSIBLESTRUCTURES 2,990,796 7/1961 Cole et al 114/.5 T 3,535,884 lO/l970 Chaney61/46.5 [761 Inventors: NaFImaIKB'FdY, 6L ummlt 3,592,155 7/1971Rosenberg 114/.5 T Northolt, Mlddlesex; Shirley Bowers 3,698,198 10 1972Phelps 6l/46.5 tu s, 3, irkdal Rd, Ealing, 3,708,987 1 1973 Roulet 61 46Longdon, W5, both of England 3,766,583 10/1973 Phelps 114/.5 X 3,793,8422/1974 Lacroix.... 6l/46.5 Flledl 28, 1973 3,824,795 7 1974 MO 61/46.521 Appl. No.2 345,757

Primary ExaminerJacob Shapiro [30] Foreign Application Priority DataAttorney, Agent, or Fzrm-Enc H. Waters et 211.

Apr. 4, 1972 United Kingdom 15546/72 [57] ABSTRACT [52] US. Cl (SI/46.5;61/50 511 lm. c1..... E02b 17/00; 865g 5/00; B65d 11/00 A z b f g f fifi g l 58] Field Of Search 61/46.5 46 50- 220/18- Sm 6 ewa e l14/5 1talners on a base, a per1meter wall on the base, and a column extendingfrom the base to above water level, the containers, wall and columnbeing formed of rein- [56] References Clted forced concrete.

UNITED STATES PATENTS 2,938,353 5/1961 Vorenkamp 6l/46.5

12 Claims, 9 Drawing Figures Patented June 3, 1915 3,886,753

5 Sheets-Sheet 1 Patented June 3, 1975 3,886,753

5 Sheets-Sheet 2 Patented June 3, 1975 3,886,753

5 Sheets-Sheet 3 Patented June 3, 1975 3,886,753

5 Sheets-Sheet 4 Patented June 3, 1975 3,886,753

5 Sheets-Sheet 5 FIG-.9

SUBMERSIBLE STRUCTURES This invention relates to submersible structuresand is particularly concerned with such structures that can be utilizedas containers for storing fluids, such as oil under water, or assupporting structures for platforms, buildings and/or plants.

According to the present invention there is provided a submersiblestructure that can be floated to a desired location and then caused tosink so as to rest on the water bed, the structure comprising aplurality of reinforced concrete hollow containers upstanding from areinforced concrete cellular base, a reinforced concrete perimeter wallalso upstanding from the base, and at least one reinforced concretehollow column extending from the cellular base to above water level inuse of the structure, there being valves and ducting extending from theinteriors of the containers and the cellular base to services situatedinside the column, whereby, from the floating condition, the structurecan be caused to sink by supplying ballast water to the space betweenthe containers and the outer perimeter wall, to the interior of thecellular base and to the interiors of the containers, and whereby thestructure can be refioated by pumping these zones dry. The reinforcedconcrete structure can be wholly or partially prestressed.

For a better understanding of the invention and to show how the same maybe carried into effect, reference will now be made, by way of example,to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side view, half in section, of a reinforcedconcrete submersible structure that serves as an underwater storagecontainer that can be floated to a desired location and then caused tosink to rest on the water bed,

FIG. 2 is a part plan view showing sectors of the structure taken on thelines II-IIA and II-IIB of FIG. 1,

FIGS. 3 to 6 illustrate how the structure of FIGS. 1 and 2 is caused tosink from a floating condition to rest on the water bed,

FIG. 7 illustrates how the structure is operated whilst resting on thewater bed,

FIG. 8 is a schematic illustration of an installation including thestructure of FIGS. 1 to 7, and

FIG. 9 is a diagrammatic side view, partly in section, of another formof structure.

The structure shown in the Figures has a container part made up of sixshort hollow reinforced concrete cylindrical containers 1 which may beprestressed if required. Each of these containers has an outercylindrical wall 1A and a central column 18 which in the formillustrated is of cruciform section. The column 1B can, of course, be ofother section, for example annular. The column 18 supports a top slab1C. The top slabs 1C of the containers 1 are interconnected by ahorizontal ring beam 1D.

The cylindrical containers 1 are supported on a cellular reinforcedconcrete or prestressed concrete raft base 2 made up of a lower slab 2A,an upper slab 2B and vertical walls 2C extending at right angles to eachother, these walls 2C connecting the upper and lower slabs whereby theinterior of the raft is divided into individual cells. These individualcells are interconnected by bores 3 to enable ballast water to flow fromone cell to another, as required, or to allow the cells to be emptied ofwater by pumping, the diamter of the bores being such as to limit theflow so as to preserve adebase and also supported at intervals bycounterforts 5. I

This wall 4 is also extended below the lower slab 2A of the raft to forma key 68 around the perimeter. The keys 6A and 68 may be of castellatedform as illustrated, depending upon the nature of the water bed.

In the form of FIGS. 1 to 8, a single, central, reinforced concrete orprestressed concrete hollow cylindrical column 7 extends from the top ofthe raft base 2 and supports a platform 8 that can serve for helicopterlandings and other purposes, at a level that is above, with thestructure resting on the water bed, the highest anticipated water levelat which the structure is to be operated, fenders 9 (at a level toextend from below to above the anticipated greatest range of tides),platforms or decks for plant and machinery 10, a surge tank 11 for oil,and an oil separator chamber 12. In the form illustrated the column 7 issupported by spokes 13 radiating to the tops of the containers 1 butthese can be omitted.

Ducts l4 connect the bottom of each container 1 to riser ducts 15,within the column 7, that connect the ducts 14 to a first manifold (notshown) connected to the separator chamber 12 by further ducts. Furtherducts 16 extending through the radial spokes 13 connect the tops of thecontainers 1, via further riser ducts 16A within the column 7 andconnected to a second manifold (also not shown), to the oil surge tank11 this second manifold being connected to the tank 11 by a duct 168. Anoil inlet pipe 17 (FIG. 7) extending from outside the perimeter of thestructure at its base to the foot of the column 7 and up the column 7 isconnected to the duct 16B above the second manifold.

The particular structure shown will stand where the highest anticipatedwater level is approximately metres above the water bed, and has astorage capacity of 500,000 barrels of crude oil. The overall diameterof the raft base 2 is 103 metres, and the height of the cylinders l is38.5 metres above the water bed. It will be appreciated that thesedimensions relate to this one example only, and alternative dimensionscan be selected as desired.

The structure can be conveniently constructed in two stages, oralternatively it may be constructed completely in one stage in a deepercofferdam. The first stage of construction can be completed in a shallowdyked basin or cofferdam where the raft base 2 and part of the perimeterwall 4 are built utilizing conventional reinforced and prestressedconcrete techniques. The partly-built structure can then be floated byflooding the basin with water and subsequently the partlybuilt structuremay be towed to a sheltered deeper water site. Conventional reinforcedand prestressed concrete techniques may then be used to complete thestructure, save for parts such as the helicopter landing platform,working platforms and other ancillary parts, in this location whilstafloat.

The thus-completed structure is trimmed as necessary for verticality byballasting the individual containers l with water as necessary to placethe structure in the condition illustrated in FIG. 3, in which Figure(and throughout FIGS. 4 to 6) G indicates the centre of gravity of thestructure, B indicates its centre of buoyancy and M its metacentre.

In the condition of FIG. 3, the structure is stable an can be towedalong a prepared channel into deeper water and thence to its intendedoperational location. To this end, towing pads can be provided atappropriate locations on the tops of the containers 1. Once the intendedoperational location is reached, submerging can commence under controlof the towing craft. The first stage in the submerging operation is toallow ballast water to enter the space above the raft base 2 between thecontainers 1 and the perimeter wall 4. Alternatively, and dependent uponthe design, water may be allowed to enter the base raft cells completelybefore being admitted to the upper tray, via holes or perforations inthe upper slab. This is effected by operating valves 19 disposed at thebase of the perimeter wall 4 and operable from the top of this wall.When this stage has been completed the structure is in the conditionshown in FIG. 4. It may be noted that for this example FIG. 4 has beendrawn showing the water levels equal on either side of, the perimeterwall. In other cases it may be more convenient to allow the waterexternally to overtop the wall before the water internally has risenthus far. The second stage in the submerging procedure is to allowballast water to enter the spaces inside the cellular raft base 2. Thisis effected by operating valves (not shown) in the bases of thesecontainers and operable from the tops of the containers or elsewhere,vent lines (not shown) being provided to allow air to escape duringballasting. When this is completed the structure is in the conditionillustrated in FIG. 5. The final stage in the submerging procedure is toopen valves (not shbwn) to allow water to enter the containers 1 (ventedvia the ducts 16) to ballast the structure until the structure comes torest on the water bed, as illustrated in FIG. 6. Throughout thesubmerging operation the structure is always under control and can bebrought to the surface at any time by reversing the entire process andpumping out ballast water via pumps (not shown) connected to ducting(also not shown). These pumps can be those that are installedpermanently, or only temporarily whilst submerging or re-floating isbeing carried out.

After the structure has reached the water bed the containers 1 areentirely filled with water to give negative buoyancy to the structureand allow the raft base 2 to bite into the water bed. The central columnmay be maintained dry if required for suitable plant environment.

Sand ballast (FIG. 7) may then be introduced if necessary in the spaceabove the raft base 2 between the containers 1 and the perimeter wall 4to make the structure safe against disturbing forces caused by theenvironment in which it is to operate. The working platforms, helicopterlanding platform and other ancillary work (not shown in FIG. 7, in whichFigure other parts have also been omitted or shown diagrammatically) arethen completed and the structure made ready to receive crude oil forstorage.

It will be appreciated that a detailed sea bed exploration has to beundertaken since a reasonably level area is required in order that thestructure does not rest at a very large angle of tilt, although therecan be provision for adjustment of the levels of the working platforms,helicopter landing platform and so on. The ground bearing pressureimposed by the structure if bedding uniformly is in the range kN/m tokN/m If the water bed is too soft or uneven, then some form of levellingmay be needed, eg in the form of a gravel bed.

Once the structure is sited at a desired location, the pipe 17 isconnected to a production platform 21 (FIG. 8) and oil is introducedinto the tops of the containers 1 via the pipe 17, the duct 168, themanifold connection (not shown) with the ducts 16A, and the ducts l6.Surges in oil supply are accommodated by the surge tank 11. The oilbeing lighter than water floats on the water in containers 1 displacingit through the ducts 14 and 15 to the separator chamber 12 from where itis pumped out to the sea by pumps on one of the plant room decks 10.When the containers 1 contain oil to a depth of 2 metres or thereaboutsabove the top of the raft base, supply of oil is stopped. The containersare emptied by pumping oil from the tops of the containers via ducts l6and 16A and the pipe 17, water entering the bases of the containers viathe ducts 15 and 14 from the separator chamber 12, the separator chamberbeing replenished with sea water by the pumps. The oil passing along thepipe 17 is pumped through meters on the production platform 21 and via asingle point mooring 22 (FIG. 8) to a tanker 23.

During operation, the level of water in the separator chamber 12 ismaintained below the level of the water outside the structure in orderto reduce bursting forces on the structure due to the stored crude oil,that is the bursting force due to the storage of liquids is reduced oreliminated by the external hydrostatic pressure.

When it is desired to move the structure to another location, the storedoil is first pumped out and any emulsion removed. The sand ballast, ifany, is then taken out and water ballast pumped out using the pumpspreviously used for submerging (reinstalled if necessary) in reverseorder from the submerging operation, until the structure floats at therequired draught. It may then be towed to the required new location.

The structure of FIG. 9 is, in many respects, similar to that describedabove and parts differing only in details are identified by thereference numerals already used and will not be again described. In thisform the single central column 7 of the form of FIGS. 1 to 8 is replacedby four columns 7A disposed at the corners of a square just inboard ofthe containers 1, of which there are, in this form, only four alsodisposed at the four corners of a square. The columns 7A contain ductingand piping (not shown) similar to that already described and support, attheir upper ends, a platform or deck 8A mounted on the column 7A throughsupport beams 24 and having plant and pump rooms and crew livingquarters and the like thereon. Braces 25 extend between the columns 7Aat intervals along the length thereof, there being a foot bridge acrossat least one of the uppermost braces 25. A further difference is that inthis particular example there is in each of the individual cells of thebase 2 central upright strut 27. The construction and manner ofoperation of the structure of FIG. 9 is otherwise similar to that of thestructure of FIGS. 1 to 8.

In other applications than as already described, structures such asdescribed above can be utilized merely as platform supportingstructures, from which a wide variety of operatiions can be carried out.

lt will be appreciated that since the structures described above arealmost entirely of concrete, they have the inherent advantage ofadequate weight. This obviates the need for anchoring the structures tothe water bed with piles, since the large uplift forces. due to the oilstored and waves, can be safely resisted by the deadweight of thestructure. This can be particularly useful in location where the waterbed is of soft materials.

Facilities for single-point mooring of tankers can be incorporated ifrequired.

Although the structure of the FIGS. has been described in connectionwith the storage of oil, it will be appreciated that such a structurecan be used for the underwater storage of any fluids that are lighterthan water.

We claim:

1. A submersible structure that can be floated to a desired location andthen caused to sink so as to rest on the water bed, the structurecomprising a reinforced concrete cellular base, a pluraliity ofreinforced concrete hollow containers upstanding from said reinforcedconcrete cellular base, a solid reinforced concrete perimeter wall alsoupstanding from the base and completely encircling said containers toform an upwardly open interior space which is capable of holding water,at least one reinforced concrete hollow column extending from thecellular base to above water level in use of the structure, valves andducting extending from the interiors of the containers and the cellularbase to services situated inside the column, whereby, from the floatingcondition, the structure can be caused to sink by supplying ballastwater to said interior space between the containers and the outerperimeter wall, to the interior of the cellular base and to theinteriors of the containers, and whereby the structure can be refloatedby pumping these zones dry and a separator chamber in said columnconnected by said ducting to said containers, said separator chamberbeing at a level in said column to be below the water level in thesubmerged condition of the structure to reduce by external hydrostaticpressure, the bursting forces due to the storage of liquid in saidcontainers.

2. A structure as claimed in claim 1, wherein the cellular base consistsof a lower slab, an upper slab and upright walls connecting the slabstogether so as to divide the base into individual cells.

3. A structure as claimed in claim 2, wherein said individual cells areinterconnected by bores to enable limited flow of said ballast waterfrom cell to cell.

4. A structure as claimed in claim 2, wherein some of said upright wallsextend below the lower slab to form keys.

5. A structure as claimed in claim 2, wherein the lower slab is shapedto form bearing areas disposed to suit the conditions of the water bed.

6. A structure as claimed in claim 2, wherein said perimeter wallextends below said lower slab to form a key around the perimeter of thebase.

7. A. structure as claimed in claim 4, wherein the keys are ofcastellated form.

8. A structure as claimed in claim 1, wherein there is only onereinforced concrete column which is disposed centrally of the hollowcontainers.

9. A structure as claimed in claim 1, wherein the con crete containersserve as buoyancy chambers during towing and submergence, supports forsaid column, and provide for the storage of liquids.

10. A structure as claimed in claim 1, wherein there is a plurality ofspaced-apart reinforced concrete columns.

11. A structure as claimed in claim 1, wherein the upper end of thereinforced concrete column serves as a platform support.

12. A structure as claimed in claim 1 further comprising a surge tank insaid column, said separator chamber and surge tank being disposed abovethe level of said hollow containers, said ducting including a first ductmeans connecting said separator chamber to said containers at the bottomthereof and a second duct means connecting said surge tank to saidcontainers at the top thereof; and means connected to said surge tankfor supplying thereto or removing therefrom a liquid which can be storedin the containers above the level of water therein.

1. A submersible structure that can be floated to a desired location andthen caused to sink so as to rest on the water bed, the structurecomprising a reinforCed concrete cellular base, a pluraliity ofreinforced concrete hollow containers upstanding from said reinforcedconcrete cellular base, a solid reinforced concrete perimeter wall alsoupstanding from the base and completely encircling said containers toform an upwardly open interior space which is capable of holding water,at least one reinforced concrete hollow column extending from thecellular base to above water level in use of the structure, valves andducting extending from the interiors of the containers and the cellularbase to services situated inside the column, whereby, from the floatingcondition, the structure can be caused to sink by supplying ballastwater to said interior space between the containers and the outerperimeter wall, to the interior of the cellular base and to theinteriors of the containers, and whereby the structure can be refloatedby pumping these zones dry and a separator chamber in said columnconnected by said ducting to said containers, said separator chamberbeing at a level in said column to be below the water level in thesubmerged condition of the structure to reduce by external hydrostaticpressure, the bursting forces due to the storage of liquid in saidcontainers.
 1. A submersible structure that can be floated to a desiredlocation and then caused to sink so as to rest on the water bed, thestructure comprising a reinforCed concrete cellular base, a pluraliityof reinforced concrete hollow containers upstanding from said reinforcedconcrete cellular base, a solid reinforced concrete perimeter wall alsoupstanding from the base and completely encircling said containers toform an upwardly open interior space which is capable of holding water,at least one reinforced concrete hollow column extending from thecellular base to above water level in use of the structure, valves andducting extending from the interiors of the containers and the cellularbase to services situated inside the column, whereby, from the floatingcondition, the structure can be caused to sink by supplying ballastwater to said interior space between the containers and the outerperimeter wall, to the interior of the cellular base and to theinteriors of the containers, and whereby the structure can be refloatedby pumping these zones dry and a separator chamber in said columnconnected by said ducting to said containers, said separator chamberbeing at a level in said column to be below the water level in thesubmerged condition of the structure to reduce by external hydrostaticpressure, the bursting forces due to the storage of liquid in saidcontainers.
 2. A structure as claimed in claim 1, wherein the cellularbase consists of a lower slab, an upper slab and upright wallsconnecting the slabs together so as to divide the base into individualcells.
 3. A structure as claimed in claim 2, wherein said individualcells are interconnected by bores to enable limited flow of said ballastwater from cell to cell.
 4. A structure as claimed in claim 2, whereinsome of said upright walls extend below the lower slab to form keys. 5.A structure as claimed in claim 2, wherein the lower slab is shaped toform bearing areas disposed to suit the conditions of the water bed. 6.A structure as claimed in claim 2, wherein said perimeter wall extendsbelow said lower slab to form a key around the perimeter of the base. 7.A structure as claimed in claim 4, wherein the keys are of castellatedform.
 8. A structure as claimed in claim 1, wherein there is only onereinforced concrete column which is disposed centrally of the hollowcontainers.
 9. A structure as claimed in claim 1, wherein the concretecontainers serve as buoyancy chambers during towing and submergence,supports for said column, and provide for the storage of liquids.
 10. Astructure as claimed in claim 1, wherein there is a plurality ofspaced-apart reinforced concrete columns.
 11. A structure as claimed inclaim 1, wherein the upper end of the reinforced concrete column servesas a platform support.